The invention relates to an interlock system and more particularly, to an interlock system using a cheater proof optical sensor.
Various techniques have been used to minimize operator exposure to safety hazards such as moving parts, electrical charge or chemicals during machine operation. In this regard the use of safety interlock switches to inhibit machine operation with covers or doors open with the related exposure to safety hazards is well known in the prior art. For example, in current use are plunger type switches in which an electrical contact is changed by the movement of the plunger in response to the movement of the door or cover. See also the magnetic type switch units such as disclosed in U.S. Statutory Invention Registration H43 published Apr. 1, 1986.
A difficulty with the prior art devices is the relative ease in which interlock switches can be cheated or rigged in order to inhibit the appropriate signal from being conveyed when a door or cover is opened. For example, in a plunger type switch, a foreign object can be inserted between contacts to simulate that a cover is closed, when, in fact, the cover is open.
It is an object of the present invention, therefore, to provide a new and improved interlock switch that is not easily cheatable yet can be easily integrated into an existing system. Another object of the present invention is to provide an optical interlock switch that is dependent upon the length of an optical path and periodic pulsing of an LED for accurate operation. Still another object of the present invention is to provide an interlock switch that is physically secured and located in the machine to prevent tampering and to inhibit false signals. Further advantages of the present invention will become apparent as the following description proceeds and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.